ISSUE 9 June 26, 2003
RECENT RAINS WILL FAVOR LEAF AND HEAD DISEASES
Moderate to heavy rains across portions of ND, MN and SD this past weekend will increase relative humidity and hours of leaf wetness on small grain crops. Risks of infection by fungal pathogens will increase and most likely be high! Although the drying "gale-force" winds of June 19-20 greatly reduced risk for those days, the heavy rains on June 21-23 shot the risk back up, with much of the crop in the heading to flowering stages coinciding where heavy rains occurred.
Growers and crop advisors should access crop growth stage, yield potential and disease risk, and then make the appropriate fungicide decision. The disease risk information is provided by the NDSU disease forecasting site at:
IPM DISEASE SURVEY RESULTS, 6/20/03
NDSU’s IPM field scouts surveyed 105 wheat and 28 barley fields during the week of June 16-20. Tan spot was observed in 68% of the fields surveyed, with the highest severity on the top leaves at 11%. Leaf rust was observed in Trail Co., while southeast and southcentral counties, site of leaf rust observations during the previous week, were NOT included in the 6/16 to 6/20 survey (see other disease observations, below). Two fields of wheat had low levels of loose smut.
Spot blotch and net blotch were commonly observed in barley fields. Levels of these leaf spots will increase with recent rains.
LEAF RUST AND OTHER DISEASE OBSERVATIONS, 6/16 - 6/23/03
An agronomist from Richland Co., ND reported on June 23th that wheat leaf rust is rapidly developing on susceptible wheat cultivars in the southeast corner of the state. Levels went from trace amounts to 10-15% severities in about 6 days. Other reports from the Sanborn area, west of Valley City, indicate increasing levels of wheat leaf rust. Remember, wheat leaf rust is an explosive disease, and infections may have already occurred and not be noticeable for several days. If rust pustules are present on the leaves below the flag leaf, the flag leaf is at risk.
During the Field Crop Management School at Carrington, ND on June 18, I observed wheat leaf rust at low levels in winter wheat plots, plus a few leaves with stripe rust. Marty Draper, SDSU Extension Plant Pathologist, reports severe stripe rust in winter wheat in southern counties in SD.
Septoria infections were observed on several varieties in the winter wheat plots at Carrington on June 18. Infections were bundant and severe on the flag leaf. Barley yellow dwarf virus was confirmed in several small grain samples sent to the Diagnostic Lab. This virus is transmitted by grain aphids, and is a threat primarily to late seeded grain, if aphids transmit the virus to the crop while it is still in the early leaf stages.
The Cereal Rust Bulletin #7, June 18, 2003, reports that wheat leaf rust was severe in the southern part of Kansas in late May on susceptible cultivars. Low to moderate leaf rust severities were found in wheat fields in eastern Nebraska the second week of June. South Dakota reported low levels of leaf rust on flag leaves of hard red winter wheat in east central SD by mid-June and some leaf rust on spring wheat cultivars in the SD nursery.
Barley scald was observed by Blaine Schatz and Greg Endres in barley variety plots at the Carrington Research Extension Center. No stem rusts of wheat or barley were reported and no leaf rust of barley was reported in the region. Crown rust of oats has not yet been reported on oat crops in the region.
Extension Plant Pathologist
KEEP AN EYE OUT FOR ANTHRACNOSE OF DRY BEAN
Anthracnose of dry bean, caused by the fungus Colletotrichum lindemuthianum, was first found in North Dakota in the 2001 growing season, and very few fields were infected in 2002. The wet conditions that have been occurring lately in eastern North Dakota are ideal for anthracnose development. The disease is seedborne, prefers wet and cool (65-80 degrees) conditions for development, and can occur at any crop stage.
Symptoms of anthracnose can appear on the leaves, petioles, and pods. Leaf symptoms may appear as dark brown lesions that follow the vein pattern of the leaf (Fig. 1). In wet weather, masses of spores that are pink to orange in color may appear in the lesions. These spores may be spread to other parts of the field, if cultivation occurs while the leaves are wet.
The first step in controlling the disease is to plant certified disease-free seed. Seed treatments are not effective in eradicating the seedborne fungus. Most of the bean varieties grown in North Dakota are susceptible. Foliar fungicides such as Bravo, Topsin M, Quadris, and Headline are registered for control of anthracnose, but no data is available for their efficacy on this disease from NDSU researchers.
Fig. 1. Anthracnose lesion following the vein pattern on a bean leaf (Photo courtesy Dr. Luis del Río).
Carl A. Bradley
Extension Plant Pathologist